I know its not the same location, or even region, but I had a slightly similar thing a couple of months back in Stoke. Leaving a parlour I noticed a police car parked opposite and two uniformed officers getting stuff out of the boot. They looked at me but didn't say anything and then as I got into the car they casually walked into the parlour. It didn't seem to be any kind of raid as there was only two of them, they stood around outside for a while in uniform and a marked car, and they were clearly in no rush to charge inside.
Just that police were in the area doesn't mean any reason to panic, although I admit my heart rate did jump a bit when I first saw them.